1. Field of the Invention
The present invention relates to sheet material handling systems, and more particularly to devices for separating signatures.
2. Background Art
The binding and printing industries often rely on high-speed sheet material handling systems for printing, collating signatures and binding the collated signatures. A typical system includes a stack of signatures, a separator, a sucker arm, a feed drum and a conveyer for collating signatures. The separator separates signatures from a stack of signatures. The sucker arm draws the separated signature towards the feed drum. The feed drum rotates, griping the separated signature and delivering it to the conveyer. The conveyer transports the signature for collation, binding and other operations, for example. Typically, a common drive mechanism drives the separator, sucker arm, feed drum and the conveyer.
Throughput depends on how closely together the signatures are spaced, and on how fast the signatures are moved. Accordingly, throughput may be optimized by spacing signatures as closely together as possible and by maximizing system speed.
Rotational speed of the separator disk is of fundamental importance to handling system performance. The faster the separator disk can rotate from the position where it enters the stack of signatures to a second position where a signature is separated, the better system throughput can be.
In an apparent attempt to overcome limitations to higher throughput rates, a sheet material handling apparatus is disclosed in U.S. Pat. No. 5,531,433 to Hawkes et al. This disclosure is incorporated herein by reference. Hawkes et al. recognize the problem of minimizing velocity mismatch between the conveyer and the feed drum. The proposed solution is to provide a rotatable ring member around a feed drum. The ring member rotates to have a velocity close to that of the conveyer. Hawkes et al. address the velocity mismatch between the conveyer and the feed drum.
Assuming that the Hawkes et al. feed drum delivers signatures faster and more reliably than a standard feed drum, the separator for the Hawkes et al. apparatus must operate fast enough to keep the feed drum properly supplied with signatures. Simply speeding up an existing separator may not be effective because the common drive mechanism may require the feed drum and the sucker bar to operate at a rate proportional to the separator speed. Accordingly, a faster way of delivering signatures to the feed drum is desired.
In typical handling systems having an array of feeders, the common drive mechanism includes a mechanically driven shaft and the array of separators and the feed drums are chain driven by the shaft to rotate at a rate proportional to the rate of shaft rotation. Such shaft driven systems are not always easily adjustable. Fine tuning the operation of the separator, feed drum and sucker arm takes time and effort. As a result, optimizing throughput is not a simple task, particularly when the handling system feeders feed signatures of various sizes.
U.S. Pat. No. 5,499,803 to Farr discloses a shaft driven material handling system having an array of feeders, the disclosure of which is incorporated herein by reference. The Farr system is broken into subsystems having discrete signature feeders. Each sub system operates on a separate drive shaft. Accordingly, each subsystem can be optimized independently to maximize throughput rates. Farr, however, fails to disclose a way of individually optimizing the feeders. Accordingly, what is desired is an improved way of feeding signatures that optimize handling system throughput.